The invention relates to a method and a system for monitoring telephone calls, in which a useful signal (which contains the call information of a telephone call) and a data set (which contains at least one digital subscriber tag) are supplied to a recording centre, and the call information is stored there in the form of digital call data and the data set associated with such call data.
Mobile communication, using radio telephones, which are also called mobile stations in the following text, is playing an increasingly important role in telecommunications. For example, in Europe, a digital mobile communications network has been set up which is based on the GSM Standard. The number of mobile subscribers who use this mobile communications network has been rising at an amazing rate in the recent past.
The enormous progress in the field of mobile communications is now resulting in a situation in which criminals, for example members of organized crime syndicates, are now increasingly using the advantages of this new technology for planning and carrying out their illegal machinations. The investigating authorities are therefore interested, while complying with the legal regulations, in also being able to monitor those telephone calls which a target person who is subject to observation makes via a mobile station.
At the moment, monitoring of telephone calls in the area of the Federal Republic of Germany is controlled by the so-called Telecommunications Monitoring Order, in accordance with which, a telephone call which is to be monitored is recorded in a recording centre which is controlled by an investigating authority. The useful signal, which essentially represents the information content of a telephone call, that is to say which contains the relevant call information, and data which are combined in a data set and are suitable for identifying the target person, that is to say, for example, the international mobile subscriber telephone number of the mobile station used, called MSISDN, for short, are supplied to the recording centre. In the recording centre, the useful signal is stored in the form of digital call data and the data set is stored, so that an authorized person requiring the information, for example a criminal investigator who has the task of monitoring the target person, can monitor the recorded telephone call. At this point, it should be mentioned, that, in the following description, the term xe2x80x9cmonitoringxe2x80x9d should not be understood just to be the assessment of an acoustic signal, but, in general, the reception and evaluation of the call information.
The known monitoring method has the disadvantage that the person who needs to do the monitoring can monitor the call made by the target person only at the location of the recording centre. In particular, it is impossible for him simultaneously to follow and to monitor the target person who, for his part, by using the mobile station during the telephone call, does not need to stay at a fixed location. This considerably limits the efficiency of the monitoring process, and the fight against crime associated with it.
The object of the invention is to specify a method and a system which allow the monitoring of telephone calls, in particular of mobile subscribers to be monitored as well, to be carried out more efficiently.
The invention achieves this object by a method in which the data set is coupled to a fixed network. The data set is compared in the [lacuna] with comparison data sets which each contain at least one comparison tag. If the subscriber tag matches the corresponding comparison tag of a selected comparison data set, a communications link is produced via a fixed network, between a relaying device, which is coupled to the fixed network, and at least one monitoring device, which is intended for monitoring the telephone call.
The call data stored in the recording centre are supplied to the relaying device. The monitoring device is supplied by the relaying device, and via the communications link, with a relayed signal which contains the call information.
The relaying device which is coupled to the call without any significant time delay. By virtue of the coupling to the fixed network, the relaying device can produce the communications link to the monitoring device directly, and can send the call data requested from the recording centre to the monitoring device in the form of a relayed signal. Irrespective of whether the fixed network is an at least partially analogue telephone network or a digital telephone network, the relayed signal may be an analogue signal or a digital signal. In the latter case, the call data can be passed on from the relaying device essentially unchanged to the monitoring device. The invention thus allows so-called on-line transmission of the telephone call to be monitored, while this telephone call is still taking place.
The relaying device offers the capability to distribute the telephone calls received by the recording centre to individual persons who need to do the monitoring. A person who needs to do the monitoring, for example a criminal investigator entrusted with monitoring the target person, is therefore not forced to monitor the target person from the recording centre, as in the past. Particularly if a mobile station is used as the monitoring device, he can monitor the target person while tracking him, thus making the fight against criminals more effective and more flexible than in the past. Using the mobile station as a monitoring device also offers the person who needs to do the monitoring the advantage of easy handling as well as virtually perfect cover as an innocent mobile subscriber.
The method according to the invention is not limited to the situation just explained, in which the target person is using a mobile station. It can likewise be used to monitor telephone calls which the target person makes via a stationary telephone. Furthermore, a stationary telephone can be used as the monitoring device. The invention thus provides a monitoring method which can be applied to all practically relevant call and monitoring situations.
The method according to the invention makes it possible to monitor a mobile subscriber without having any involvement in the radio transmission which takes place between the mobile subscriber""s mobile station and a base transmitting/receiving station of the mobile communications network. This is a major advantage, since the signals interchanged between the mobile station and the base transmitting/receiving station are encrypted, and monitoring of these signals involves major complexity. If one also considers that coupling of the relaying device to the recording centre on the one hand and to the fixed network on the other hand can be carried out without any major technical complexity, then it becomes clear that the proposed method is also highly cost-effective.
In an advantageous development of the invention, a telephone number which is contained in the selected comparison data set and is allocated to the monitoring device is dialled by the relaying device in order to produce the communications link. The information given by the stored telephone number makes it possible for the relaying device to produce the connection directly to the person who needs to monitor the target person, so that the person carrying out the monitoring can monitor the telephone call without any significant time delay.
When the communications link is being produced between the relaying device and the monitoring device of the person who needs to do the monitoring, it is possible to access control data which are contained in the selected comparison data set. The control data can be produced specifically for each person who needs to do the monitoring, that is to say for each individual comparison data set, thus ensuring that calls are set up flexibly and in an individually optimized manner. Further control data contained in the comparison data set allow additional information to be transmitted to the monitoring device. Thus, for example, after producing the communications link, predetermined, individually produced text sequences can be played to the person who needs to do the monitoring, providing him with information about the target person to be monitored.
The information content of a telephone call can be stored in the recording centre by means of a digital recording device. If the useful signal supplied to the recording centre is an analogue signal, then the recording device can convert this signal into digital call data.
If the target person is a mobile subscriber, then the data set may contain, for example, the international mobile subscriber telephone number MSISDN, the international mobile radio set tag IMEI and/or the international mobile subscriber tag IMSI. One of the tags mentioned above may be used as the subscriber tag. Furthermore, a number of these tags can be used at the same time.
The relaying device may, for example, be connected to the recording centre via a local data network, also called a LAN. The recording centre sends the call data and the data set via this data network to the relaying device. Particularly fast data transmission is possible by using a LAN.
The interface between the relaying device and the fixed network may be an interface specified in accordance with the known ISDN Standard. The interface may be configured as an S0 interface or, if more powerful communication is desired, as an S2M interface.
In a further advantageous development of the invention, once the communication link has been set up, the monitoring device emits an identification tag to the relaying device, which is compared with a corresponding comparison tag contained in the comparison data set. This makes it possible to prevent an unauthorized subscriber from being able to monitor the telephone call.
Such an identification tag is, for example, a personal identification number, also called a PIN number, which is transmitted using the DTMF method. The PIN number can advantageously be decoded at the interface between the relaying device and the fixed network.
According to a further aspect of the invention, a system is provided for monitoring telephone calls.